bitbake: Use a "fork" multiprocessing context

Python 3.14 changes the default multiprocessing context from "fork" to
"forkserver"; however bitbake heavily relies on "fork" to efficiently
pass data to the child processes. As such, make "fork" context in the bb
namespace and use it in place of the normal multiprocessing module.

Note that multiprocessing contexts were added in Python 3.4, so this
should be safe to use even before Python 3.14

[YOCTO #15858]

(Bitbake rev: 62be9113d98fccb347c6aa0a10d5c4ee2857f8b6)

Signed-off-by: Joshua Watt <JPEWhacker@gmail.com>
Signed-off-by: Richard Purdie <richard.purdie@linuxfoundation.org>

bitbake/lib/hashserv/tests.py

@@ -10,7 +10,7 @@ from .server import DEFAULT_ANON_PERMS, ALL_PERMISSIONS
 from bb.asyncrpc import InvokeError
 import hashlib
 import logging
-import multiprocessing
+from bb import multiprocessing
 import os
 import sys
 import tempfile